Dynamic channel quality measurement procedure implemented in a wireless digital communication system to prioritize the forwarding of downlink data

ABSTRACT

A wireless digital communication system includes a base station in communication with a plurality of user equipment mobile terminals (UEs). The system prioritizes the forwarding of blocks of downlink data to designated ones of the UEs. The system employs adaptive modulation and coding (AM&amp;C) to achieve improved radio resource utilization and provides optimum data rates for user services. Blocks of downlink (DL) data are received by the base station which requests downlink (DL) channel quality measurements only from those mobile terminals (UEs) with pending downlink transmissions. The UEs respond to the request by measuring and reporting DL channel quality to the base station, which then allocates resources such that the UEs will make best use of radio resources. The base station notifies the UEs of the physical channel allocation indicating the modulation/coding rate and allocated slots followed by transmission of blocks of downlink data which are transmitted to the UEs.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/029,569, filed Dec. 21, 2001, which claims priority fromU.S. Provisional Patent Application No. 60/290,877, filed May 14, 2001,which applications are incorporated herein by reference.

BACKGROUND

[0002] The present invention relates to wireless digital communicationsystems. More particularly, the present invention relates tocommunication stations which employ code-division multiple access (CDMA)technology. Specifically, the present invention relates to determiningradio conditions for use in optimizing radio resource utilization aswell as selecting data rates for user services.

[0003] In code-division multiple access (CDMA) third generation (3G)cellular telecommunication systems, adaptive modulation and coding(AM&C) techniques are applied to transmissions in order to achieveimproved radio resource utilization and provide increased data rates foruser services under appropriate conditions. These AM&C techniques takeinto account radio conditions in advance of transmissions in order todetermine modulation and coding rates that take the greatest advantageof current radio propagation conditions utilizing these techniques.

[0004] Utilizing these AM&C techniques, a procedure is required thatprovides a physical channel quality measurement from the receiver inadvance of each transmission. Based on this quality measurement, thetransmitter determines the appropriate modulation and coding rate forthe particular transmission.

[0005] In CDMA systems, as with any wireless systems, radio conditionscan change rapidly due to a wide variety of both natural and man-madeconditions. Since the channel quality measurement is used to determinetransmission modulation and coding, and since channel quality changesrapidly due to the changing conditions of the transmission path, theperformance of the adaptive transmission process is directly related tothe length of the time period between when the channel qualitymeasurement is performed and when the transmission is initiated.

[0006] Physical or logical control channels are then used to transferthe channel quality measurements from the receiver to the transmitter.Channel quality signaling may utilize either dedicated control channelsto each user equipment (UE) or common control channels shared by allUEs. A UE may be a cellular phone, PDA (personal data assistant) or anyother type of wireless device. When dedicated control channels are used,a continuous signaling channel is available over time for propagation ofchannel quality measurements for each UE. This is an optimal solutionfor AM&C since the quality measurement is continuously available.Transmissions can occur at any time, taking into account thecontinuously available quality measurement for appropriate modulationand coding settings. Additionally, with a dedicated control channelalways available in the uplink, the channel can be also used to supportlow rate uplink data transmissions.

[0007] The difficulty with the dedicated control channel approach isthat physical resources are continuously allocated even when there is nodata to transmit. A primary application of AM&C techniques is non-realtime high data rate services, for example, Internet access. For theseclasses of service, the best quality of service (QoS) is achieved withshort, high rate transmissions with relatively long idle periods betweeneach transmission. These long idle periods result in an inefficient useof dedicated resources.

[0008] The problem can be minimized with pre-configured periodicdedicated channel allocations. But this results in periodic availabilityof quality measurements. If the quality measurements are notcontinuously available, for UEs which have transmissions at any onepoint in time, only some portion of the UEs will have recent channelquality measurements.

[0009] Another alternative is the use of common control channels. Withcommon control channels, a continuous signaling channel exists that isshared between all UEs within the cell. Procedures are defined fordetermining each UEs access to the common control channel. UE identitiesare used to distinguish UE specific transactions.

[0010] The difficulty with the common control approach for support ofAM&C is the large amount of signaling overhead necessary to administrateeach UE's access to the control channel. As aforementioned, UEidentities are required to distinguish UE specific transactions.Additionally, to avoid contention-based access to the uplink commoncontrol channel, individual allocations are required to be signaled onthe downlink common control channel for each UE's access. Since uplinktransmissions cannot always be predicted, periodic allocations of theuplink control channel must be signaled on the downlink common controlchannel, which results in considerable signaling overhead. Also, thecommon control approach does not provide for low rate, uplink datatransmissions.

[0011] In summary, the efficient performance of AM&C techniques isprimarily based on the availability of recent physical channel qualitymeasurements from the receiver in advance of each transmission.Optimally, measurements are available with minimal latency for all userswith active data transmissions. The dedicated control channel solutionprovides continuous measurements, but since transmissions arediscontinuous, this is an inefficient use of radio resources. Periodicconfigured dedicated control channels minimize the radio resourcerequirement, but this increases measurement latency. The common controlchannel method can provide measurements on a continuous or periodicbasis, but the signaling overhead results in an inefficient use of radioresources.

[0012] There exists a need for a system that provides channel qualitymeasurements with low latency and low signaling overhead.

BRIEF DESCRIPTION OF THE DRAWING(S)

[0013] The objectives of the present invention will become apparent uponconsideration of the accompanying detailed description and figures, inwhich:

[0014]FIG. 1 is a flow chart illustrating one preferred Dynamic ChannelQuality Measurement Procedure (DCQMP) of the present invention.

[0015]FIG. 2 shows an alternative embodiment of the DCQMP of the presentinvention shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0016] Presently preferred embodiments are described below withreference to the drawing figures wherein like numerals represent likeelements throughout.

[0017]FIG. 1 is a flow diagram which illustrates the dynamic channelquality (CQ) measurement procedure 60 of the present invention which maybe implemented by a wireless digital communication system having a basestation/node B (hereinafter base station 12) which communicates with atleast one UE 30. Although it is intended for the presently inventivemethod to support communications between a base station and a pluralityof UEs, for simplicity the following description will detail the stepsperformed by a single UE, it being understood that other UEs willoperate in a similar manner.

[0018] Blocks of downlink (DL) data are transferred to the base station12 which are designated for a particular UE 30 (step S1).

[0019] The base station 12, responsive to receipt of downlink data andin advance of a transmission to the UE 30, requests DL CQ measurementsonly from a UE 30 having pending downlink transmissions (step S2).

[0020] The UE 30 receives the request and makes the requested CQmeasurement at step S3 and reports the DL CQ measurement to the basestation 12 at step S4.

[0021] Based on the CQ measurement reports received from each UE (stepS5), the base station 12 determines which of the UEs will make the bestuse of radio resources, and determines which slots to use (step S6).Preferably, the UEs are prioritized by their CQ so that the UE with thehighest CQ is sent its data first and then the UE with the secondhighest CQ is sent its data second, and so on until the UE with thelowest CQ is sent its data last.

[0022] Since the CQ measurement requests and the responsive CQmeasurement reports are only generated when needed, the signalingoverhead required for a common control channel is greatly reduced.Measurement reports are available for all active transmitting users,similar to the dedicated control channel case, but avoiding the resourceinefficiency during idle periods.

[0023] The priority of transmissions is determined according to the DLCQ measurements, and the DL physical channel allocation is signaled tothe appropriate UEs, indicating the particular coding rate, modulationtype and allocated slots (step S7). The designated UE receives thecoding rate, modulation type and allocated slots (step S8), and setsthese parameters for reception (step S9).

[0024] Blocks of downlink data are then transmitted by the base station12 to the designated UE 30 (step S10) a given, but short, time afterperformance of step S7 to enable the UE 30 time to set up for reception.The UE 30 receives the downlink data (step S11) at the specified codingrate, modulation type and in the allocated slots specified at step S7.

[0025] The present invention thus provides the fundamental requirementsfor AM&C operation while maintaining the most efficient use of radioresources. Since DL CQ measurements are available with the minimumpossible latency for all transmissions, the choice of the best user(s)to provide service in the next transmission time frame is optimized.Additionally, measurements provided by periodic or continuous mechanismsdo not provide increased benefit, performance gain or enhancement overthe present invention.

[0026] Implementation of the present invention also minimizesmeasurement processing and the associated power consumption, especiallyimportant in the UE, which is typically powered by a small power sourceof limited capacity, (i.e. a chargeable battery). Since a qualitymeasurement is only requested for a particular active transmission, thenumber of required measurements are minimized.

[0027] In accordance with an alternative embodiment of the method 70 ofthe present invention shown in FIG. 2, only certain quality measurementsmay be required depending on the radio resources used for a particulartransmission. For example, in the 3G standards, the CQ for only specificphysical timeslots may be requested. Therefore, the number ofmeasurements performed is reduced by limiting the requirement of a CQmeasurement to only active transmissions and, depending on the scale ofthe transmission, only requiring measurement on particular radioresources, (i.e., specific time slots). This is shown in FIG. 2, whichis similar to FIG. 1 except for modified steps S2A and S3A, whichreplace steps S2 and S3 respectively of FIG. 1. In step S2A, the basestation 12 requests the UE 30 to perform a measurement only on aparticular radio resource. In response, the UE performs the DL CQmeasurement on the specified radio resource (step S3A).

[0028] The present invention provides many advantages over prior artschemes. First, the invention provides the highest efficiencyutilization of the air interface since only those UEs having pendingtransmissions will be required to respond to a request for DL CQmeasurements. This permits the overhead signaling to be at a minimum.

[0029] Second, since the transmissions are prioritized according to thehighest quality DL CQ measurements, the highest data rates permissiblewill be achieved for each time slot or multiple time slots.

[0030] Third, since UEs are only required to respond to the request forthe DL CQ measurements, unnecessary measurements by the UEs will not berequired, thereby saving the battery life of the UEs.

[0031] A final advantage of the present invention is the increasednumber of users that may be supported in a cell for both of the methodsdisclosed herein. The number of users that are supported is limited inthe dedicated control channel method by the requirement for dedicatedradio resources; and in the common control channel method by signalingoverhead requirements. By limiting the measurement signaling proceduresto active users, the present invention minimizes the common controlsignaling overhead and supports the greatest number of users in thecell.

[0032] While the present invention has been described in terms of thepreferred embodiment, other variations which are within the scope of theinvention as outlined in the claims below will be apparent to thoseskilled in the art.

What is claimed is:
 1. A wireless digital communication system forprioritizing the forwarding of blocks of downlink data, the systemincluding a base station and a plurality of user equipment mobileterminals (UEs), the system comprising: (a) means for the base stationto receive blocks of downlink data for distribution to designated onesof the plurality of UEs; (b) means for the base station to transmit toeach of the designated UEs a request for a downlink channel qualitymeasurement to be performed; (c) means for each of the designated UEs toperform the downlink channel quality measurement; (d) means for each ofthe designated UEs to transmit the results of the downlink channelquality measurement to the base station; (e) means for the base stationto establish a priority for the designated UEs based on the results ofthe downlink channel quality measurements; (f) means for the basestation to transmit an allocation signal to each of the designated UEs;(g) means for each of the designated UEs to set up transmissionparameters in response to the allocation signal; and (h) means for thebase station to transmit the downlink data to the designated UEs inaccordance with the established priority.
 2. The system of claim 1wherein the allocation signal indicates a particular coding rate,modulation type and at least one allocated slot.
 3. The system of claim1 wherein the designated UEs have pending downlink transmissions.
 4. Ina wireless digital communication system including a base station andplurality of user equipment mobile terminals (UEs), a method forprioritizing the forwarding of blocks of downlink data, the methodcomprising: (a) the base station receiving blocks of downlink data fordistribution to designated ones of the plurality of UEs; (b) the basestation transmitting to each of the designated UEs a request for adownlink channel quality measurement to be performed; (c) each of thedesignated UEs performing the downlink channel quality measurement; (d)each of the designated UEs transmitting the results of the downlinkchannel quality measurement to the base station; (e) the base stationestablishing a priority for the designated UEs based on the results ofthe downlink channel quality measurements; (f) the base stationtransmitting an allocation signal to each of the designated UEs; (g)each of the designated UEs setting up transmission parameters inresponse to the allocation signal; and (h) the base station transmittingthe downlink data to the designated UEs in accordance with theestablished priority.
 5. The method of claim 4 wherein the allocationsignal indicates a particular coding rate, modulation type and at leastone allocated slot.
 6. The method of claim 4 wherein the designated UEshave pending downlink transmissions.
 7. A wireless digital communicationsystem for prioritizing the forwarding of blocks of downlink data, thesystem including a base station and a plurality of user equipment (UEs),the system comprising: (a) means for the base station to transmit toeach of the UEs a request for a downlink channel quality measurement tobe performed; (b) means for each of the UEs to measure and report theresults of the downlink channel quality measurement to the base station;(c) means for the base station to transmit a downlink physical channelallocation signal to the UE associated with the highest reporteddownlink channel quality measurement; (d) means for the UE associatedwith the highest downlink channel quality measurement to set uptransmission parameters based on the allocation signal; and (e) meansfor the base station to transmit at least one block of the downlink datato the UE associated with the highest downlink channel qualitymeasurement.
 8. The system of claim 7 wherein the allocation signalindicates a particular coding rate, modulation type and at least oneallocated slot.
 9. The system of claim 7 wherein the UEs have pendingdownlink transmissions.
 10. In a wireless digital communication systemincluding a base station and plurality of user equipment mobileterminals (UEs), a method for prioritizing the forwarding of blocks ofdownlink data, the system including a base station and a plurality ofuser equipment (UEs), the method comprising: (a) the base stationtransmitting to each of the UEs a request for a downlink channel qualitymeasurement to be performed; (b) each of the UEs measuring and reportingthe results of the downlink channel quality measurement to the basestation; (c) the base station transmitting a downlink physical channelallocation signal to the UE associated with the highest reporteddownlink channel quality measurement; (d) the UE associated with thehighest downlink channel quality measurement setting up transmissionparameters based on the allocation signal; and (e) the base stationtransmitting at least one block of the downlink data to the UEassociated with the highest downlink channel quality measurement. 11.The method of claim 10 wherein the allocation signal indicates aparticular coding rate, modulation type and at least one allocated slot.12. The method of claim 10 wherein the UEs have pending downlinktransmissions.